Measurement of complexing agent concentration in an electroless plating bath

Abstract

The concentration of citrate complexing agent in an electroless cobalt or nickel plating bath is determined by titrating a sample of the electroless plating bath containing a small concentration of free fluoride ion with a standard lanthanum nitrate solution. During the titration, La 3+ ion first reacts preferentially with the citrate complexing agent and then with fluoride ion, which reduces the free fluoride ion concentration. The endpoint for the titration is indicated by a substantial decrease in the free fluoride ion concentration, which is detected via a fluoride ion specific electrode (ISE). The method can be used for analysis of other complexing agents.

1. A method for determining the concentration of a complexing agent in an electroless plating bath, comprising the steps of:
 providing a test solution comprising a sample of the electroless plating bath and a predetermined concentration of fluoride ion;  
 titrating the test solution with a titrant solution comprising a predetermined concentration of a complexing metal ion;  
 detecting a substantial decrease in the concentration of fluoride ion in the test solution via a fluoride ion specific electrode; and  
 calculating the concentration of the complexing agent in the electroless plating bath from the volume ratio of the test solution required to produce the substantial decrease in the concentration of the fluoride ion in the test solution.  
 
     
     
       2. The method of  claim 1 , wherein the electroless plating bath is of a type used to deposit a metal selected from the group consisting of cobalt, nickel, molybdenum, tungsten, rhenium, copper, gold, palladium, platinum, and alloys thereof. 
     
     
       3. The method of  claim 1 , wherein the complexing agent is selected from the group consisting of citrate, lactate, succinate, hydroxyacetate, aminoacetate, malonate, ethylenediamine, and ethylenediamine tetraacetate. 
     
     
       4. The method of  claim 1 , wherein the predetermined concentration of fluoride ion has a value in the 0.5 to 500 mg/L range. 
     
     
       5. The method of  claim 1 , wherein the predetermined concentration of the complexing metal ion is from 0.01 to 1.0 M. 
     
     
       6. The method of  claim 1 , wherein the complexing metal ion is selected from the group consisting of La 3+ , Fe 3+ , Hg 2+  and Ce 4+  ions. 
     
     
       7. The method of  claim 1 , wherein said step of detecting a substantial decrease in the concentration of fluoride ion in the test solution includes the step of generating a titration curve of fluoride ion specific electrode potential versus volume of added titrant solution. 
     
     
       8. The method of  claim 7 , wherein said step of detecting a substantial decrease in the concentration of fluoride ion in the test solution further includes the step of taking the first derivative of the titration curve. 
     
     
       9. The method of  claim 7 , wherein said step of detecting a substantial decrease in the concentration of fluoride ion in the test solution further includes the step of taking the second derivative of the titration curve. 
     
     
       10. The method of  claim 1 , wherein the test solution further comprises a buffer solution. 
     
     
       11. A method for determining the concentration of a complexing agent in an electroless plating bath, comprising the steps of:
 providing a test solution comprising a sample of the electroless plating bath and a predetermined concentration of fluoride ion;  
 titrating the test solution with a titrant solution comprising a predetermined concentration of La 3+  ion;  
 detecting a substantial decrease in the concentration of fluoride ion in the test solution via a fluoride ion specific electrode; and  
 calculating the concentration of the complexing agent in the electroless plating bath from the volume ratio of the test solution required to produce the substantial decrease in the concentration of the fluoride ion in the test solution.  
 
     
     
       12. The method of  claim 1 , wherein the electroless plating bath is of a type used to deposit a metal selected from the group consisting of cobalt, nickel, molybdenum, tungsten, rhenium, copper, gold, palladium, platinum, and alloys thereof. 
     
     
       13. The method of  claim 11 , wherein the complexing agent is selected from the group consisting of citrate, lactate, succinate, hydroxyacetate, aminoacetate, malonate, ethylenediamine, and ethylenediamine tetraacetate. 
     
     
       14. The method of  claim 11 , wherein the predetermined concentration of fluoride ion has a value in the 0.5 to 500 mg/L range. 
     
     
       15. The method of  claim 11 , wherein the predetermined concentration of the of La 3+  ion is from 0.01 to 1.0 M. 
     
     
       16. The method of  claim 11 , wherein said step of detecting a substantial decrease in the concentration of fluoride ion in the test solution includes the step of generating a titration curve of fluoride ion specific electrode potential versus volume of added titrant solution. 
     
     
       17. The method of  claim 16 , wherein said step of detecting a substantial decrease in the concentration of fluoride ion in the test solution further includes the step of taking the first derivative of the titration curve. 
     
     
       18. The method of  claim 16 , wherein said step of detecting a substantial decrease in the concentration of fluoride ion in the test solution further includes the step of taking the second derivative of the titration curve. 
     
     
       19. The method of  claim 11 , wherein the test solution further comprises a buffer solution. 
     
     
       20. A method for determining the concentration of citrate complexing agent in an electroless plating bath, comprising the steps of:
 providing a test solution comprising a sample of the electroless plating bath and a predetermined concentration of fluoride ion;  
 titrating the test solution with a titrant solution comprising a predetermined concentration of La 3+  ion;  
 detecting a substantial decrease in the concentration of fluoride ion in the test solution via a fluoride ion specific electrode; and  
 calculating the concentration of the citrate complexing agent in the electroless plating bath from the volume ratio of the test solution required to produce the substantial decrease in the concentration of the fluoride ion in the test solution.  
 
     
     
       21. The method of  claim 20 , wherein the electroless plating bath is of a type used to deposit a metal selected from the group consisting of cobalt, nickel, molybdenum, tungsten, rhenium, copper, gold, palladium, platinum, and alloys thereof. 
     
     
       22. A method for determining the concentration of citrate complexing agent in an electroless cobalt or nickel plating bath, comprising the steps of:
 providing a test solution comprising a sample of the cobalt or nickel electroless plating bath and a predetermined concentration of fluoride ion;  
 titrating the test solution with a titrant solution comprising a predetermined concentration of La 3+  ion;  
 detecting a substantial decrease in the concentration of fluoride ion in the test solution via a fluoride ion specific electrode; and  
 calculating the concentration of the citrate complexing agent in the electroless plating bath from the volume ratio of the test solution required to produce the substantial decrease in the concentration of the fluoride ion in the test solution.  
 
     
     
       23. A method for determining the concentration of citrate complexing agent in an electroless cobalt or nickel plating bath, comprising the steps of:
 providing a test solution comprising a sample of the cobalt or nickel electroless plating bath, a buffer solution, and a predetermined concentration of fluoride ion;  
 titrating the test solution with a titrant solution comprising a predetermined concentration of La 3+  ion;  
 detecting a substantial decrease in the concentration of fluoride ion in the test solution via a fluoride ion specific electrode; and  
 calculating the concentration of the citrate complexing agent in the electroless plating bath from the volume ratio of the test solution required to produce the substantial decrease in the concentration of the fluoride ion in the test solution.